Composition comprising methylol starch propionamide and thermosetting resin and process for cross-linking same



United States Patent() CGMPGSITION CGMPRTSING NETHYLOL STARQH 1963; Divided and this application Aug. 7, 1961, Sen

3 Claims. (Cl. 260-172) This invention relates to potentially reactive starch derivatives which form clear water resistant films, surface coatings and adhcsive'bonds. More specifically this invention relates to methylol starch propionamide ethers prepared from formaldehyde and starch propionamide and to their use in various applications. Said methylol derivatives when cured alone or in combination with amineor phenol-formaldehyde monomers or partially condensed polymer-storm films, surface coatings and adhesive bonds which are water insoluble or resist hydra tion by water.

It is an object of this invention to provide a new starch derivative. A further object is to provide a new starch derivative which will form, on curing, films orcoatings which will resist rehydration in water,

Another object of this invention is to prepare potentially thermosetting methylol 'derivatives of starch from formaldehyde and starch propionamide ether. Yet another object isto prepare said methylol propionamide derivatives under conditions so that substantially no crosslinking of the starch occurs during the methylolation reaction. A further object is to prepare said methylol starch derivatives by treating starch propionamide in past ed form with formaldehyde at pH of 7-11. A further object is to prepare said methylol starch derivatives by methylolating' the starch propionamide in granule form. A still further object is the preparation of films, surface coatings, fiber laminates and moldings from said methylol starch propionamides either alone or in combination with aminoplast and phenolic resin forming m aterials. A further object is to prepare waterproofing adhesives by forming the methylol starch propionamide in situ by reac- '2 Water insoluble films can be produced by heat curing of the methylol propionamide products at any pH from about 3 to 13. Since formaldehyde is firmly bound to the starch derivatives herein described, and therefore does not exist as free or easily freed formaldehyde, health hazards'due to formaldehyde vapor are minimized. The

methylol propionamide derivatives are stable if stored at 7 pH 7l0 at ambient temperatures, whereas starch-formaldehyde mixtures lose formaldehyde on storage.

It is old in the art to prepare waterproofing adhesives from mixtures of starch and various phenoand aminoplast resins. When such adhesives. are cured insolubilization results, primarily from polymerization of the resin component rather than from interaction of the resin with starch. That is, two methylol groups will interact much more readily than will a methylol group and a starch hydroxyl. resin may be effected only by using vigorous curing conditions, i.e., high temperature at an acid pH. These conditions are not practical for many applications. Thus,

, under the most practical curing. conditions, starch in a starch-resin matrix does not undergo sufiicient cross-link.

tion of starch with acrylamide and formaldehyde. Other objects will appear hereinafter. I

Our invention is based upon the discovery that starch propionamide, activated with chemically bound methylol groups, may be cured under relatively mild conditions either alone or in combination with various aminoplast or phenoplast resins to. form tough, adhesive .and cohesive films-or coatings whichresist rehydration in-water.

The methylol starch propionamides are. distinguishable in several respects from products which have been prepared by treating starch with formaldehyde. One.pri mary diiference is the manner in which formaldehyde is 'bound to starch. Formaldehyde in. themethylol starch propionamide is firmlyboundto the amide nitrogen group.

by a primary chemical bond. The methylol group cannot be removed from the starch propionamide either by washing'with water or treating with sodium sulfite. On the'other hand, if raw starch is treated with formaldehyde under our conditions for methylolation, all the formaldehyde can be removed by either of the above; treatments.

Adhesives of. methylol starch propionamide cure faster and form more insoluble films or coatings under a given set of conditions than films prepared from starch and formaldehyde. Said films are tougher, more pliable and cohesivethan films prepared from ordinary starches alone or from mixtures of starch and an aminoplast resin.

ing. to. resist at least some rehydration in Water. Therefore, it would be desirable to activate starch so that interaction between the activated starch and resin occurs reads ily under relativelyfmild curing conditions. Our invention contemplates activating starch with chemically bound polymerizable groups which will combine or polymerize with aminoand phenoplast resins so that starch becomes an integral'part of the cured: starch-resin matrix. When used with formaldehyde resins,.the resulting ad hesives cure faster and form more insoluble films, coatings and fiber laminates than compositions in which starch and formaldehyde replace methylol starch propionamide. Furthermore, we have discovered that methylol starch propionamide is compatible with formaldehyde resins in that tough, clear and nonbrittle films can be prepared from such combination.

The methylol products are particularly useful as the adhesive in paper. coating colors Where high wet-rub resistance combined with unusually high wax pick is desired; Because methylol starch propionamide derivatives possess both good adhesive and cohesive qualities, exceptional cohesion of' coating color to paper and of coating to clay particles occur. These properties. are achieved withmethylolstarch propionarnide alone or in combination with: a thermosetting resin, such as, melamineor ureaforrnaldehyde. It is significant that exceptionally strong adhesion of coating'color to paper is obtained with methylol starch propionamide in both the thermally cured and,

uncured coatings. Methylol starch propionamides alone or in-combinawith an aminoplast resin such as trimethylol melamine can be insolubilized on the fabric to the extent that it is not removed after-repeated washings. In an example to, follow it is shown thatthere is no'decrease in stiffnessor loss in. weight of size when a cotton fabric sized with methylol starch propionarnide. is subjected to five successive washings.

One serious problem in the manufacture of acoustical tile using a mixture of mineral wool and'starch paste is thatthe baked product sags in a humid atmosphere. This is due to rehydration of starch at high moisture levels. Since thermally cured films of methylol starch propionamide do not rehydrateto an appreciable extent, the prod uct is potentially useful in this application.

Starch propionamide ethers most suitable for preparing.

methylol starch propionamide have been described in application Serial No. 734,101; filed May 9, 1958, now

Some chemical interaction between starch and 3 U.S. Patent No. 2,928,827. There a process is described for the preparation and purification of starch propionamide ethers at relatively high propionamide D.S. levels Which contain substantially no carboxyethyl groups. Starch is reacted under non-gelatinizing and non-swelling conditions with acrylamide in an aqueous medium containing alkali and sodium sulfate, the amount of alkali not exceeding 0.1 mole per mole of starch and the amount of sodium sulfate being at least 0.05 mole per mole of starch. After the reaction is complete, the pH of the reaction mixture is adjusted to 2.0 to 4.5 and the starch ether washed with water and recovered. The presence of a large number of carboxyethyl groups is generally undesirable in uses where high water resistance is needed as they exert a solubilizing effect on the cured film. However, we do not wish to be bound by any particular ratio of propionamide to carboxyethyl groups. Starch propionamide ether suitable for the invention may be prepared by reacting starch with acrylamide in aqueous alkaline medium at a pH of at least 9.5. The following equations illustrate the preparation of: (1) starch propionamide ether, and (2) methylol starch propionamide.

ll pH 7-11 StarCh-O-CHrCHrC-NH: ECHO Both the rate of cure and degree of insolubility obtained increase with the number of methylol groups present on the starch propionamide. In general, We find that from about 2 to 50 methylol groups per 100 anhydroglucose units is satisfactory to form a water insoluble film or coat ing. To obtain the above methylol degree of substitution, it is necessary that the number of propionamide groups range from about 3 to about 75 propionamide groups per 100 glucose units. However, we do not wish to be bound by any limitation with respect to degree of substitution, or method of preparation of the parent starch propionamide.

Our invention is applicable to all starches and starch fractions but is particularly applicable to propionamide ethers prepared from raw starch and acidor enzymemodified corn and Waxy starches. Specifically, it is applicable to the propionamides of corn, potato, tapioca, sago, rice, wheat, waxy maize, grain starches in raw or modified form, e.g., modified with acids, enzymes or oxidizing agents. It is also applicable to the propionamide of amylose and amylopectin, the components of corn starch.

' The proportion of amide groups which can be methylolated varies with reaction time and temperature as Well as pH of the reaction medium. In general, satisfactory results are achieved by methylolating at a temperature ranging from about 40 to 70 C. at a pH of 9 to 11.0 for periods ranging froml to 3 hours. These variables are, to some extent, interdependent so that by proper manipulation, methylolation can be effected by operating outside of the above ranges. We prefer, however, to methylolate at about 50 C. at pH 10 for 2 hours.

The efiiciency of methylolation increases with concentration of starch propionamide. Therefore, it is generally desirable to methylolate at the highest workable starch concentration. For example, the maximum workable starch concentrations may vary from about 10 percent for thick-boiling starch propionamide to about 40 percent for highly converted thin-boiling starch propionamide.

In general, We find it desirable to use from about 1 to about 1.5 moles formaldehyde per mole of propionamide substituent to perform the methylolation. Under these conditions about 50 to 75 percent of the propionamide The data in Table I show that when the mole ratio of formaldehyde to propionamide groups is increased from 0.25 to 2.5 mole of formaldehyde combined per mole of propionamide group is increased from 0.16 to 0.79. The data also show that raw corn starch does not combine with formaldehyde to form a stable methylol product. The methylol starch propionamide pastes in all experiments were clear, viscous and not cross-linked. Furthermore, the pastes did not set back or undergo bacterial attack upon standing at least 12 months at ambient temperature.

The following experiment is typical.

Reagents: Reagent quantities (mole) 60-fluidity starch propionamide Water 13.8

Sodium hydroxide 0.0027

Formaldehyde 0.062

The starch propionamide ether Was pasted by cooking 15 minutes in a round-bottom, three-necked reaction flask provided with agitator, thermometer and reflux condenser. The paste was cooled to 50 C. caustic soda added to raise the paste pH to 10.1, formaldehyde added and the paste stirred at 50 C. for 2 hours. Unreacted or free formaldehyde was quanitatively determined by the sulfite method (LP. Walker, Formaldehyde, pages 3 82-383, 2nd edition, 1953, Reinhold Bublishing Co., New York). The difference between formaldehyde added and free formaldehyde is a measure of formaldehyde bound as methylol groups.

Table I.INFLUENCE OF FORMALDEHYDE CONCEN- 'TRATION ON STARCH PROPIONAMIDE REACTION EFFICIENCY Moles ECHO per mole of starch Exp. No. Parent starch billed Uncombined starch propionde.

EXAMPLE 2 I This example illustrates a typical preparation of methylol starch propionamide from starch propionamide. The latter was prepared fromipasted corn starch. Both the impure reaction product and the purified product were methylolated.

Preparation 0 Starch Propionamide From Pregelatinized Starch One mole, 162 grams DB. of 60-fluidity acid modified corn starch was slurried in 1100 ml. of water and cooked for 15 minutes on a steam bath. The paste was cooled to. about 60 C. and 0.06 mole of NaOH added to raise the pH to 12.6. Then, 0.6 mole (43 grams) of acrylamide was added; The paste was stirred 16 hours at 52 C. and the pH reduced to 8.5 by addition of 2 N HCl.

The product was divided into two portions, A and B. Portion A was methylolated without additional purification. Portion B was freeze dried and thoroughly washed with methanol to eliminate impurities before methylolating. The pure product analyzed .35 D.S. withrespect to propionamide groups based on Kjeldahl nitrogen analysis.

Methylolation of Unpurified Starch Propionamide Five-tenths mole (670 ml;) of aliquot A (above) was heated to 50C., then 26 ml. of 38 percent aqueous formaldehyde and sufiicient NaOH to raise the pH to 10.0 were added. This amount of formaldehyde is equivalent to 1.1 moles per mole of acrylamide used in the propionamide reaction. The paste was stirred in a closed container at. 50 C. for 2 hours. The pH dropped to 9.15 during reaction. The product analyzed 0.26 D.S. with respect to methylol groups onstarch and on unreacted acrylamide.

Methylolalion 0f Purified Starch Propionamide About 0.14 mole (27.3 grams) of portion B was dispersed to 280 ml. of water. Sufiicient aqueous formaldehycle was then added to obtain 1.5 to 1 ratio of formaldehyde to propionamide groups. The pH wasadjusted to 10.6 with NaOH and the paste stirred at 50 C. for 3 hours. The. final pH was 10.2. The product was 0.24 D.S. with respect to methylol groups.

EXAMPLE 3 EXAMPLE 3a This example illustrates the methylolation of starch. propionamide in the semidry form. To 98 grams of 018 D5. granular starch propionamide at 7.5 percent 1noisture was added 5.55 grams of powdered paraformaldehyde. The mole ratio of formaldehyde to propionarnide groups was 1.72. Two' grams of powdered anhydrous sodium carbonate was thenladded and the mixture blended: thoroughly in a Waring Blendor. After blending, the mixture analyzed 4.88 percent formaldehyde by the sulfite method. A 25 gram portion of the mixture was intro- 7 duced to aSprengel pressure flask and sealed. The flask and contents were placed in a C. constant temperature bath for 16 hours. The flask was then cooled to 25 C. and the mixture analyzed'for free formaldehyde. 'An. average value of 3.53 percent formaldehyde was found showing that 1.35 percent of the original formaldehyde was bound as methylol starch propionamide. This amount is equivalent to'0.48 mole formaldehyde bound per mole of propionarnide.

-' EXAMPLE 4 This example compares the effect of acidic and alkaline pH catalysts for curing cast films of methylol starch propionamide. A 0.24 13.8., -F starch propionamide paste at 10 percent starch solidswas methylolated with various quantities of formaldehyde. The pH of'the methylolated paste was adjusted with alum, HCl or NaOH to the desired value and films cast on stainless steelv plates. The filmswere cured one hourat 80 C., ground and extracted with water at 60 C. The weight of the insoluble residue was then determined.

In experiment 43 unreacted formaldehyde was removed product with methanol, by chemical methods whereby a,

formaldehyde reactive substance such as sodium sulfite is added, or. by using low amounts of formaldehyde for methylolation.

Table IL-INSOLUBLES OF METHYLOL STAROH PRO- ,PIONAMIDE FILMS CURED AT C. FOR ONE HOUR Mole HCHO per Insolubles mole propiouamide Percent Experiment Catalyst Paste dry basis number pH extracted Used Oornat 60 C.

bined 1 Excess HCHO removed by dialysis.

EXAMPLE 5 This example illustrates the use of methylol starch propionamide alone'and in combination witha commercial thermosetting resin to impart a permanent finish to cotton fabrics. The methylol starch propionamide employed was prepared from a 0.24 D.S., 60-fluidity starch; propionamide. The derivative was methylolated with 1.5 moles formaldehyde per mole of propionamide group. .The

product was 0 .17 D.S. with respect to methylol groups.

The following procedures wereused for sizing and measuring the permanency of the size on cotton cloth:

PADDING SoLUrroN 1 percent methylol starch-propionamide (based on wt. of bath). t I

10 percent Zeset S resin which is a melamine-ureaforrnaldehyde'resin (based on Wt. of bath) 0:25 percent tartaric acid (based on Wt.,0f resin).

(Resin and catalyst not used where starch is used alone.) i

NEUTRALIZATION BATH.

0.1 percent soda ash (based on wt. of bath). 0.05 percent Duponol D paste which is a surface active agent-of'the alcohol sulfate type (based on wt. of bath).

FINISHING PROCEDURE Cotton cloth 80 inches x 80 inches was sized with the padding solution, and excess liquid removed with squeeze I rolls. The swatch was dried on a mangle iron at about 200 F.,'then cured one minute at 325350 F. The fabric, was first rinsed in the neutralization bath, then rinsedrin clear water and finally dried on a mangle iron.

WASHING CYcLE' only exceptionally high after 5 washings (86 mg..-cm.')

but is also greater than initially (80 mg.-cm.) observed.

This example illustrates a typical preparation of methylol starch propionamide in granule form from starch propionamide. The latter was prepared in granule form from unmodified corn starch following procedures described in US. Patent No. 2,928,827.

Preparation of Granule Methylol Starch Propionarnide from Granule Starch Propionamide One mole, 163.4 grams DB. of granule starch propionamide, 0.02 D.S;, was slurried in 534 grams of Water in which had been dissolved 44.5 grams of anhydrous sodium sulfate. To this mixture there was added 2.25 milliliters formalin and 70 milliliters of N sodium hydroxide.. This reaction mixture, approximately pH 10.0, con-- tained in a three-necked flask provided with agitator, thermometer and reflux condenser was placed in a 50 C. constant temperature bath. The reaction mixture was sampled and analyzed for formaldehyde prior to placing in the bath. Analysis showed 0.111 percent of formaldehyde to be present. After agitating the reaction mixture at 50 C. for 2 hours, the free formaldehyde content had dropped to 0.0957 percent. These results show that 0.207 mole of formaldehyde had combined per mole of propionamide. After 24 hours, 0.425 mole of formaldehyde had combined.

EXAMPLE 7 This example illustrates the preparation of methylol starch propionamide in granule form and the use of the methylol product as a waterproof adhesive for paper.

Two-tenth mole of acrylamide and 0.14 mole Na SO were added to one mole of raw corn starch (180 grams at 12 percent H O) in 200 ml. of water. Then, 0.0 8

a strip of kraft paper. A second strip of kraft paper was glued on the sized strip with a hand iron set at 320 F. The bonded paper did not separate when boiled in water for 10 minutes. Strips of kraft paper similarly bonded with the parent starch propionamide separated within 30 seconds in the boiling water.

EXAMPLE 8 This example illustrates the use of methylol starch propionamide in clay coating colors to improve wet-rub resistance and Dennison wax pick. The methylol derivative was prepared from pasted 60-F, 0.24 D.S. starch propionamide. Methylol D.S. was 0.16.

A clay slip was prepared by dispersing paper clay KCS, Georgia Kaolin Company, in Water containing 0.3 percent of sodium pyrophosphate so as to obtain 72 percent clay solids. The pasted methylol starch propionamide was added to the clay slip in an amount to give 20 percent adhesive based on clay. A solution of wool soap, 2 percent soap based on methylol starch propionamide solids, was added next and the coating color adjusted to 40 percent solids with water.

The coating was applied to coating rawstock of pounds basis weight (24 x 36/500 ream) with the following results.

Dennison wax pick air-dried cure, 24 hr., 300

F., 1 minute 11. Wet-rub resistance:

300 F., 1 minute Excellent. 300 F., /2 minute Good. 200 F., 2 minutes Slight.

Papers coated with methylol starch propionamide possess Dennison wax pick values at least 2 points higher than is encountered with conventional thin-boiling starches. Also, sufficient cross-linking of methylol starch propionamide occurs at 300 F. in the absence of a catalyst to give good to excellent wet-rub resistance.

EXAMPLE 9 This example compares the properties of clay coating colors for paper prepared using as the adhesive a standard acid modified corn starch, methylol starch propionamide, or the latter in combination with a melamine-formaldehyde resin and using ammonium chloride as the curing catalyst. Paper clay KCS stabilized with 0.3 percent tetrasodium pyrophosphate was employed in preparing the pigmentslip.

Brookfield viscometer Model LVF No. 4 spindle at 12 r.p.rn. MSP=methylol starch propoinamide. I MF Resin=methylated trirnethylolmelamme resin (Lanasct resin).

mole of NaOH in ml. of water was added while agitatingvigorously. The slurry was stirred 16 hours at 40 C.

The pH of the slurry was then reduced to pH 10.0 with HCl and 17 ml. of a37 percent aqueous solution of formaldehyde added. The slurry was stirred one hour at 45 C. The methylol product was filtered and washed with water. A cooked paste of the product was relatively. clear and fluid indicating that substantially no crosslinking of the starch granules by formaldehyde occurred during methylolation.

A 30 percent paste of the methylol starch propionamide was cooked in water and then applied in a thin film to ing adhesives can be increased with methylol starch propionamide. The greatest improvement is achieved when methylol starch propionamide is used as the carrier portion of the adhesive. The carrier is the gelatinized starch portion of a corrugating adhesive. One of its functions "is to hold ungelatinized starch in suspension so that the pionamide is used With a synthetic thermosetting resin such as urea-HCHO, ketone-HCHO or resorcinal-HCHO resin. The improvement probably results from a greater interaction of methylol starch propionamide with the resin hyde resin (U.F. Concentrate-85) containing excess formaldehyde was added and the formulation stirred 1 hour.

Considerable water resistance was imparted when the adhesive was tested in the manner described in Example 10. A formulation similarly prepared without acrylamide gave poor waterproofing results.

component than occurs when the latter is replaced with unmodified starch.

EXAMPLE 10 This experiment illustrates the use of methylol starch propionamide and resorcinol-HCHO in an alkaline setting waterproofing corrugating adhesive. In this example both starch propionarnide and resorcinol were methylolated by in situ reaction.

A slurry containing 10 grams of 0.4 B5. thick-boiling starch propionamide and 0.75 gram of NaOH in 70 ml.

of water was heated to 70 C. and stirred at this temperature for 5 minutes. To the gelatinized starch propionamide paste, 0.5 gram of resorcinal was added. The paste was stirred an additional 10 minutes at 70 C.

After cooling to about C., the carrier paste was added to a slurry of grams of raw corn starch in 135 ml. of water..- Three grams of paraformaldehyde was added and the formulation stirred 1 hour to eifect meth- -ylolation of starch propionamide and resorcinol. Two

strips of kraft paper were glued together with the adhesive by heating the sized strips 3 seconds under a 2000-gram weight. After soaking the strips in cold water for 24 hours, considerable fiber pull was noted when the strips were separated. r V

This formulation gave better waterproofing than an adhesive similarly prepared using corn starch as the carrier instead of starch propionamide.

EXAMPLE 1 1 I A slurry was prepared consisting of 10 grams of raw corn starch, 5 grams of acrylamide in 50 ml. of water. One gram of NaOH dissolved in 10 ml..of water was then added and the paste heated. 15 minutes at 68 C. The

V paste was cooled to about 40 C. and then added to a 'slurry consisting of 50 grams of raw starch in 140 ml.

of water. Then, 11 ml. of a commercial urea-formalde- EXAMPLE 12 This example illustrates the preparation of a waterproof corrugating adhesive using preformed methylol starch propionamide and a commercial urea-formaldehyde resin, sold under Urac 110.

Ten grams of thick-boiling methylol starch propionamide, 0.5 D.S. with respect to propionamide, was added to ml. of water containing 0.5 gram of NaOH. After heatig 15 minutes at 68 C. the paste was cooled to about 40 The cooled paste was slowly added to a slurry consisting of 50 grams of raw corn starch, 5 grams of Urac resin in ml. of water. After thorough mixing, 2

grams of paraformaldehyde was added and the formulamethylol, group is attached to the amide nitrogen, and.

which contains some free hydroxyl groups per anhydroglucose residue of starch, with a thermosetting resin selected from the group consisting of an amine-formaldehyde thermosetting resin and a phenol-formaldehyde thermosetting resin; the reaction being performed at a pH within the range of 3 to 13.

2. The product produced by the process of claim 1.

3. A curable composition comprising a methylol starch propionamide, in which the methylol group is attached to the amide nitrogen, and which contains some free hydroxyl groups per anhydroglucose residue of starch and a thermosetting resin selected from the group consisting of amine-formaldehyde resins and phenol-formaldehyde resins.

References Cited in the file of this patent UNITED STATES PATENTS Strain Sept. 12 1939 Moller June 24, 1941 Vaughan Nov. 18, 1952 

1. A PROCESS FOR FORMING A CROSS-LINKED, STARCH-RESIN MATRIX OF LOW ATER SOLUBILITY WHICH COMPRISES REACTING BY HEATING METHYLOL STARCH PROPIONAMIDE, IN WHICH THE METHYLOL GROUP IS ATTACHED TO THE AMIDE NITROGEN, AND WHICH CONTAINS SOME FREE HYDROXYL GROUPS PER ANHYDROGLUCOSE RESIDUE OF STARCH, WITH A THERMOSETTING RESIN SELECTED FROM THE GROUP CONSISTING OF AN AMINE-FORMALDEHYDE THERMOSETTING RESIN AND A PHENOL-FORMALDEHYDE THERMOSETTING RESIN; THE REACTION BEING PERFORMED AT A PH WITHIN THE RANGE OF 3 TO
 13. 